1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display.
2. Description of the Related Art
A liquid crystal display (hereinafter referred to as xe2x80x9cLCDxe2x80x9d) featuring low profile and light-weight has been increasingly used mainly for personal computers and cellular phones. However, since a liquid crystal which is a structural element of the xe2x80x9cLCDxe2x80x9d does not emit light by itself unlike a light-emitting type element such as a CRT, the LCD requires a separate illuminating means of observing an image. In particular, to satisfy recent growing demand for lower profile and lower electric power consumption, a thin plate-like spread illuminating apparatus of side light type (light-conductive plate type) is often used as an illuminating means for irradiating the LCD.
The applicants of the present invention disclosed one embodiment of such a spread illuminating apparatus of side light type in Japanese Patent Laid-open No. 2000-11723. FIGS. 5 and 6 show such a spread illuminating apparatus 1.
In FIG. 5, the spread illuminating apparatus 1 is generally composed of a transparent substrate 2 made of a light-transmissible material and a bar-like light source disposed along and close to an end surface 3 of the transparent substrate. The transparent substrate 2 is rectangular, is plate-like, and has a light reflection pattern 5 formed on one surface thereof (an upper side in FIG. 5).
The light source 4 is generally composed of a bar-like light conductive member 6 made of a transparent material and disposed along and close to the end surface 3 of the transparent substrate 2, and a spot-like light source 7 disposed at an end surface 6c of the light conductive member 6.
The light conductive member 6 is provided with an optical path conversion means 8. The optical path conversion means 8 includes a plurality of grooves 9 shaped, for example, triangular (as shown in FIG. 6) in section, extending in the thickness direction (vertical direction in FIG. 5) of the light conductive member 6, and located on a side surface 6b opposite to a side surface 6a facing the end surface 3 of the transparent substrate 2 and allows light rays emitted from the spot-like light source 7 to substantially uniformly enter the end surface 3 of the transparent substrate 2. To realize uniform spread emission, the depth of the grooves 9 triangular in section is set to gradually increase in proportion to the increase in distance from the spot-like light source 7.
A light reflection member 10 substantially U-shaped in section and having a light reflection layer (not shown) formed on an inner surface thereof is provided so as to cover longitudinal surfaces of said light conductive member 6 except the side surface 6a and also a proximal portion (a portion along the end surface 3) of the transparent substrate 2. The light reflection member 10 improves the efficiency of the light utilization through the light conductive member 6.
In addition to the above function, the light reflection member 10 connects the light conductive member 6 with the transparent substrate 2 by a predetermined strength.
In the spread illuminating apparatus 1, as shown in FIG. 6, light emitted into the light conductive member 6 is reflected at an inclined wall 9a defining the groove 9 along an optical axis A at the transparent substrate 2 (in the direction orthogonal to the length of the light conductive member 6) and enters the transparent substrate 2 so as to be effectively used as frontlight (FL) or backlight (BL) (that is, it becomes effective light). On the other hand, some portion of the light having entered the light conductive member 6 penetrates the inclined wall 9a, becoming leakage light B. The leakage light B having penetrated the inclined wall 9a is reflected by the light reflection member 10 with some portion thereof entering the transparent substrate 2 along the direction of the optical axis A and becoming effective light in a way mentioned above. However, since the remaining portion thereof becomes a component of an oblique direction and cannot be used as frontlight or backlight, that is, it becomes non-effective light.
On the spread illuminating apparatus 1, the characteristics of light amount were examined using a luminance meter (not shown) by varying a field angle xcex8, and the characteristic curve shown in FIG. 7 was obtained. This helps grasp the generation of the effective light and the non-effective light.
Specifically, the luminance meter is disposed over the transparent substrate 2 so as to be turnable on the central axis (not shown) extending orthogonal to the length of the light conductive member 6, and the amount of light emitted from the transparent substrate 2 is measured with the field angle (a turning angle) xcex8 being varied.
The amount of light varies in a wave-like manner according to a field angle xcex8 as shown in FIG. 7. Specifically, a large wave appears at a field angle xcex8 of 0xc2x0 or close to 0xc2x0 (hereinafter referred to as xe2x80x9c0xc2x0 neighborhood areaxe2x80x9d), a small wave appears at a field angle xcex8 of 60xc2x0 to 70xc2x0 (hereinafter referred to as xe2x80x9c60xc2x0-70xc2x0 neighborhood areaxe2x80x9d), and the line connecting the large wave and the small wave caves in.
The large wave corresponds to the effective light and the small wave corresponds to the non-effective light.
In this connection, even in the spread illuminating apparatus provided with a light conductive member 6A having an optical path conversion means 8A comprising a plurality of grooves 11 triangular in section and a plurality of flat portions 12 each formed between two adjacent grooves as shown in FIG. 8, the generation of non-effective light cannot be prevented for the reason described above, so that light cannot be effectively used as frontlight or backlight.
The present invention has been made in light of the above problems, and it is an object of the present invention to provide a spread illuminating apparatus capable of more effectively using light emitted from a light source.
In order to solve the above problems, according to a first aspect of the present invention, in a spread illuminating apparatus which includes a rectangular transparent substrate made of a light-transmissible material, and a bar-like light source comprising a bar-like light conductive member made of a transparent material and provided along one end surface of the transparent substrate and a spot-like light source disposed on an end of the light conductive member, a light reflection member, which has on a surface thereof a plurality of projections each forming a prism and having a reflection layer formed thereon so as to reflect light coming from the light conductive member, is disposed along and close to a side surface of the light conductive member opposite to a side surface facing the transparent substrate.
According to a second aspect of the present invention, in the configuration mentioned in the first aspect, the reflection layer is made of a metal film or a dielectric multi-layer film.
According to a third aspect of the present invention, in the configuration mentioned in the first or second aspect, the plurality of projections are shaped identical with one another.
According to a fourth aspect of the present invention, in the configuration mentioned in the first to third aspects, each of the projections forms a substantially triangular prism, and an angle formed by a surface of each of the projections positioned toward the spot-like light source and by a plane parallel to a major surface of the light reflection member is set to range between 20xc2x0 and 45xc2x0.
According to a fifth aspect of the present invention, in the configuration mentioned in the fourth aspect, the spot-like light source is provided on both ends of the light conductive member, and each of the projections forms an isosceles-triangular prism.
According to a sixth aspect of the present invention, in the configuration mentioned in the first to third aspects, each of the projections forms a substantially arc-shaped prism.
According to a seventh aspect of the present invention, in the configuration mentioned in the sixth aspect, the spot-like light source is provided on both ends of the light conductive member.